1. Field of the Invention
This invention relates to a guided-wave acoustooptic (AO) device and, more particularly, to a guided-wave AO device incorporating a surface acoustic wave (SAW) transducer array for wide band Bragg modulators and deflectors.
2. Description of the Prior Art
Wideband SAW transducers have been used for guided-wave AO devices such as scanners, spectrum analyzers and correlators and there are several known methods of making these wideband SAW transducers. Among these, a multiple tilted SAW transducer array configuration having individual interdigital transducers (IDT) having staggered center frequencies and being tilted to satisfy the Bragg condition has the advantages of simplicity and flexibility. However electronic phase shifters are manually required to compensate for the phase difference between diffracted light beams for adjacent transducers at the crossover frequency and to ensure that they add in phase.
A method to eliminate such electronic phase shifters by properly configuring the transducers is described in C. S. Tsai, Guided-Wave Acoustooptic Bragg Modulators for Wide-Band Integrated Optic Communications and Signal Processing, IEEE, Transactions on Circuits and Systems, Vol. CAS-26, 1072-1098 (1979). However, the equations shown therein for determining the horizontal separation and the vertical step height between each pair of adjacent transducers are not adequate, particularly when the input light beam has a large beam width. In such case, the diffraction efficiency at the crossover frequencies becomes low so that a flat diffraction efficiency over the full bandwidth cannot be obtained.